The field of the invention relates generally to gas turbine engines, and more specifically, to a method and assembly for reducing blade tip leakage in gas turbine engines.
To maintain fan airflow performance in at least some known gas turbine engines, a clearance between impeller blades of the fan and a housing or casing of the fan is set to a close distance. The tight clearance facilitates preventing reverse flow leakage around the blade tips through the tip clearance. Higher air pressure downstream of the fan impeller tends to drive the flow back toward upstream, and this is observed at the tip clearance.
In some operating conditions, such as, but not limited to, extreme operating conditions, the close clearance may result in blade-housing interference and led to failures of fan components in the field. Such interference has been addressed by trimming the blade tips to increase the clearance. However, increasing the clearance increases leakage flow around the blade tips and reduces the performance of the fan assembly. The impact on fan performance is two-fold: Reduced impeller working area and increased tip clearance that will allow flow leakage the opposite direction to the main flow. The loss in performance caused by the former can be regained to some extent by adjusting blade pitch angles, for example, by twisting the tip of each blade and letting the rest of the blade span follow.